A solid oxide fuel cell is a fuel cell comprising a plurality of anode layers and cathode layers separated from each other by means of a solid electrolyte layer. The solid electrolyte is for example zirconia that is fully or partially stabilised with yttria. Charge transfer through the solid electrolyte layer from the cathode to the anode is done by oxygen ions.
The overall cathode reaction of a solid oxide fuel cell is:½O2+2e−→O2−;and the overall anode reaction is:H2+CO+O2−→H2O+CO2+2e−.
The anode off-gas thus comprises carbon dioxide and water.
Typically in a tubular solid oxide fuel cell, off-gases, i.e. anode off-gas and oxygen-depleted air, are mixed and thus form a mixture comprising a large amount of nitrogen and small amounts of carbon dioxide, water and hydrogen. If however carbon dioxide could be obtained in a highly concentrated form, preferably above 80 vol %, it can be efficiently liquefied and subsequently used in enhanced oil recovery or the recovery of coal bed methane. Also for effective sequestration of carbon dioxide, a concentrated carbon dioxide stream is needed. Carbon dioxide in lower concentration, e.g. 50 vol %, can usefully be applied in the food and paper industry.